The present invention concerns a procedure and a means for producing an image based on contrast discrimination in an image forming means with one-dimensional or multidimensional image field.
A plurality of industrial products and functions would be easy to automate and their efficiency could be increased if a simple image forming means serving as a visual or tactile sense were available for diverse control and monitoring functions. Activities of this kind would be, for instance, optimizing the operation of lift doors or location finding among the shelf beams in a warehouse system in automated material handling.
Among the image forming means in current use, the means working with a great number of image elements are not sensible to be used in small format controlling and monitoring tasks. For instance, coding a colour TV image in real time requires approximately 85 Mbit/sec handling rate, whereas the clock frequency of a fairly fast 8- bit microprocessor is no more than 6-8 MHz. The design of the present invention is intended for small format systems with a relatively small number of image points, and it is concentrated on pre-processing the image information, which in this case can be carried out largely independent of the application objects.
Small format monitoring systems which do not use a camera or equivalent means are as a rule built around a small number of independently operating on/off sensors. The most common sensor types are the photocell, supersonic pick-ups and inductive and capacitive pick-ups. Said pick-ups have been developed to be more accurate and less expensive, whereby it has been possible to increase their number in various applications, but in those applications said sensors still operate as individuals, each with its own operating point setting. A design differing in the synchronizing of different points of measurement has been disclosed, for instance, in the European Patent Application No. 17 547, which reads on a proximity detector with six image forming points. In this design, the signals from capacitive antennas have been processed in combination, whereby an adequate change of capacitance at any one antenna produces a distinguishable change with reference to the mean change of all antennas.
The advantage of the above design in comparison with onepoint sensor applications and differentially operating twopoint sensor applications is its more extensive range of coverage. Since the outputs of the antennas are merely compared with their mean, this cannot yet be considered to represent any versatile image forming. Drawbacks of the design according to the European Pat. No. 17 547 are furthermore its high sensitivity to background capacitances in the environment, which particularly in lift applications changes from floor to floor, and poor control in special situations, for instance particularly when the lift doors are close to their extreme positions. For instance, regarding the sensitivity of the edge sensors on a lift door compromises are frequently unavoidable owing to environmental conditions, since otherwise an unreliable, over-sensitive means would be the result.
An image composed of as few as six points contains much more information than a mere deviation of mean. Means handling typically greater numbers of image points, such as photodiode arrays, have been so constructed that all image forming points have as nearly as possible the same gain. If it is desired to compose an image based on a plurality of inexpensive sensors, e.g. phototransistors, the variation of gains and soiling and other environmental factors impede any attempt at stable synchronization of the image forming points. Individual calibration of the amplifiers cannot be considered any satisfactory solution in such cases, even though a microcomputer for instance can automatically attend to this.